fix doxygen brief in subzero header files

src/IceTargetLowering.cpp

Index: src/IceTargetLowering.cpp
diff --git a/src/IceTargetLowering.cpp b/src/IceTargetLowering.cpp
index a5bd86b05edd48f06504daac0cb7d560826ffe47..171882d29e915ba511523458c99f17b3f3f8d95e 100644
--- a/src/IceTargetLowering.cpp
+++ b/src/IceTargetLowering.cpp
@@ -8,10 +8,11 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file implements the skeleton of the TargetLowering class, specifically
-/// invoking the appropriate lowering method for a given instruction kind and
-/// driving global register allocation. It also implements the non-deleted
-/// instruction iteration in LoweringContext.
+/// \brief Implements the skeleton of the TargetLowering class.
+///
+/// Specifically this invokes the appropriate lowering method for a given
+/// instruction kind and driving global register allocation. It also implements
+/// the non-deleted instruction iteration in LoweringContext.
 ///
 //===----------------------------------------------------------------------===//